The HBO Prohibition-era drama caps a compelling fourth season Sunday as treachery flows like bootleg booze.

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Nucky Thompson (Steve Buscemi) is facing tough times as the fourth season of "Boardwalk Empire" ends Sunday.

Updated at 2:32 PM EST on Friday, Nov 22, 2013

The most recent episode of "Boardwalk Empire" featured the series' most stunning moment since crime boss Nucky Thompson executed his turncoat surrogate son, Jimmy Darmody, at the end of Season 2: Jimmy's Jocasta of a mom, mistress of self-delusion Gillian, tells her lover/savior she killed her son's doppelgänger in a selfish act of self preservation.

"You can make yourself live with anything," she declared.

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Gillian uttered the most important line of the season seconds before the boyfriend who helped her kick heroin and seemed to accept her seedy past as a moll and a madam revealed himself as a Pinkerton agent and nabbed her for the murder. (Anyone who claims to have seen that Film Noir twist coming has a bigger problem with truth than Gillian.)

The shocker underscored a season filled with betrayal, much of it cloaked in a dark familial tint and soaked in blood. The scene also set the stage for Sunday's season finale, in which long-simmering treachery threatens to boil over and flow wildly through Nucky's Prohibition-era Atlantic City.

Stars Steppin' Out

The layers of betrayal, like bootleg booze, run deep on “Boardwalk Empire.” A ruthless G-man trying to get J. Edgar Hoover’s attention uses a family secret as blackmail fodder to get Nucky’s loyal manservant Eddie to flip. Eddie, after offering little information, instead flips himself out a window to his death.

The FBI agent had more luck with Nucky’s brother, Eli, back in the fold after previously ganging up on his brother with other crooks out of misplaced pride. This time, Eli reluctantly is turning on Nucky to save his own son from a murder rap. But the son, who let a college buddy take the fall for the death, might be turning on Eli to stay in Nucky’s graces.

The heart of the season pulses through an even more intricate set of relationships centering on this year’s breakout character: Dr. Valentin Narcisse, a Marcus Garvey acolyte whose Ivy League demeanor and standing as a Harlem community leader belies his role as a cutthroat gangster. His sworn enemy is Nucky’s confederate, Chalky White, a far less-polished, but no-less-savvy mob boss. They’re split by the bizarrely named Daughter – a tragic blues singer who is bound by a sordid secret past to Narcisse and by something resembling love to Chalky, who has forsaken his own family for her. She now appears to have betrayed both men.

Nucky stuck by Chalky in his feud with Narcisse. But thanks to a near deadly misunderstanding, Chalky thinks Nucky served him up for death.

In four seasons, “Boardwalk Empire” has succeeded in becoming more complex and compelling. The stellar acting, led by Steve Buscemi as Nucky, creates some tough decisions for Emmy voters, given strong performances by, among others, Jeffrey Wright (Narcisse) and Patricia Arquette, nearly unrecognizable as Sally Wheel, a southern hooch runner with a strange hold on Nucky’s damaged heart.

The real star of the show is the writing, brimming with finely wrought, intersecting plots and dialogue like Gillian’s crucial line, which can be turned into the key question of the season, if not the series: Can you make yourself live with anything?

Nucky finally isn't so sure. He calls Sally after realizing his brother is setting him up for a fall. "I want out," Nucky tells her.

But he's in too deep. And so are viewers. Check out a preview of season finale below: